1. Technical Field
The invention is related to radio frequency (RF) plasma reactors for processing semiconductor wafers, flat panel display wafer or substrates generally, and in particular to inductively coupled RF plasma reactors and improvements increasing the uniformity of the plasma ion density across the entire surface of large substrates.
2. Background Art
RF plasma reactors are employed in performing various processes on semiconductor wafers, including etching processes and chemical vapor deposition processes, for example. An inductively coupled RF plasma reactor typically has an inductive coil antenna wound around the reactor chamber and connected to a plasma source RF power supply. Such an inductively coupled plasma reactor is particularly useful because it can achieve a very high plasma ion density for high production throughput, while avoiding a concomitant increase in ion bombardment damage of the wafer.
One problem with inductively coupled plasma reactors is that the plasma ion density distribution can vary greatly, depending upon various parameters including the particular process gas or gas mixture introduced into the reactor chamber. For example, the plasma ion density may be high at the wafer center and low at the wafer periphery for one process gas, while for another process gas it may be the opposite pattern (i.e., low at the wafer center and high at the wafer periphery). As a result, the antenna design must be customized for each different process or process gas to provide an acceptable degree of plasma ion density uniformity across the wafer surface, a significant problem.
If the plasma reactor is employed in processing a large flat panel display wafer (comprising a glass substrate), for example, the large surface area of the substrate prevents achievement of good plasma ion density uniformity across the substrate surface without extraordinary care in customizing the antenna design.
It is therefore an object of the present invention to provide a uniform plasma ion density across an entire substrate surface in an inductively coupled plasma reactor without requiring installation of a completely new antenna in the plasma reactor.